Various advancements in motorized vehicles, namely motorized wheelchair technology, have enabled many persons with motor impairments and/or fatigue to be more independent; wherein the user is able to manipulate or control the movements of the wheelchair as desired without assistance from another. The implementation of programmable electronics and a variety of adaptive control devices have enabled self driving for many new wheelchair users. Despite these advancements, challenges still are encountered or presented in providing an optimal interface between the user and the control components of the wheelchair designed to control the operation of its automated systems.
The most common interface device is a single stem gimbal type joystick that is vertically oriented and attached to a support, such as an armrest. The gimbal stem is constrained to tilt approximately 30 degrees from vertical in any direction during operation. This allows for continuously variable control over direction and speed. For example, when the gimbal stem is tilted forward, a signal is sent to the wheelchair's controller that is interpreted as a forward drive command.
The joystick is usually controlled by grasping a small rubberized knob covering the end of the joystick gimbal stem. While the gimbal type of joystick is simple in design and provides an adequate control interface for many users, there are several inherent problems associated with this type of interface. To use this interface, a user must have the dexterity required to grasp the joystick to effectively manipulate the joystick as intended. Trying to manipulate a gimbal type joystick can be frustrating for an individual who has lost some or most motor skills. Because there is only a single protuberance, users with no finger dexterity usually drive with the knob between their thumb and first digit metacarpal. With little or no grasp, it is easy for the hand of a user to slip over the joystick during forward driving, and off the side of the joystick when turning.
Also, going over a small hump can cause the user to lose the grip on the joystick causing the chair to stop abruptly. This abrupt stopping could throw the user out of their chair or expose the user to danger while crossing streets. In addition, driving in reverse is impossible without repositioning the hand to apply a backwards force to the joystick. When driving backwards there are no analogous anatomic features to the thumb notch to provide effective lateral manipulation leading to poor rearwards driving control. Those with adequate motor skills may feel this type of interface device adequate, but it may be difficult and frustrating, or even dangerous for users who have little finger function. Many alternate interfaces with revolved surfaces (balls, cones, domes etc.) are available to assist those with weak grasp but they do not alleviate the described issues for those with no grasp.
Another type of interface device incorporates a handle with two protuberances rising vertically from each end of a horizontal cross member. This handle is coupled to a joystick gimbal stem medially beneath the cross member parallel to the protuberances making it medially and sagittally symmetrical. Thus the handle can be used by either hand. It is commonly referred to as a “goal post” style joystick handle. Most users rest their palms flat on the cross member between the protuberances which constrains lateral slipping of the palm. One protuberance rests in the notch between thumb and palm and the other protuberance secures the palm around the metacarpal of the last digit. The thumb remains unsupported. The goal post joystick provides significant improvement over the single protuberance joystick in that it is more ergonomically correct for the user, and requires less motor skills to manipulate effectively. The cross member serves as the primary interface for the user, with the protuberances providing additional support and functioning as secondary interface components. The user can push with the palm on the cross member to control forward motion and apply a force to the two lateral protuberances to control turning and apply corrective signals. The users fingers are positioned in front of the cross member, which in combination with increased hand contact (which leads to increased friction), facilitates backwards driving without need of hand repositioning.
Despite its advantages, one of the problems with the “goal post” joystick just described, as with the single stem gimbal joystick in that it may be uncomfortable to manipulate either type of joystick over long periods of time leading to fatigue, as both types were designed to facilitate manipulation not improve comfort. They are often fabricated by professionals such as occupational therapists for a specific user which is slow and expensive.
Another difficulty with providing an optimal handle is the changing orientation in respect to the user resulting from the gimbal stem moving through its range of motion during operation.
Many users of power wheelchairs who have hand weakness also have wrist weakness. Frequently users wear splints to improve wrist stability but the splints do not allow for wrist flexion. They also partially obstruct the palm. Other users wear apparatus' on their arms to combat contractures or spasticity. These devices do not allow the wrist to flex as the gimbal stem goes through its range of motion making it impossible to maintain full contact between handle and palm.
As such, both the single gimbal joysticks and the goal post joysticks, as described above, lack features that would optimize manipulation of the Joystick, and therefore control of the wheelchair movements.
It would, therefore, be advantageous to provide a wheel chair joystick that overcomes the deficiencies and ergonomic issues of the aforesaid devices.